1. Field of the Invention
The present invention relates to a method of manufacturing a semiconductor device and more particularly a method of manufacturing a semiconductor device having a transistor and a capacitor.
2. Description of the Prior Art
Normally, the semiconductor memory device includes memory cells. Each of the memory cells has a transistor and a capacitor connected to the transistor.
There have been demands for the next generation memory device, e.g., the gigabit DRAM, to have the capacitor being minuter size and higher capacitance.
In order to form the capacitor having such structure, dielectric material such as tantalum oxide (Ta2O5), barium-strontium-titanate ((Ba,Sr)TiO3), lead-zirconate-titanate (Pb(ZrxTi1xe2x88x92x)O3), or the like is employed. In addition, new electrode material such as strontium ruthenate (SrRuO3) may be employed.
However, there is the problem that the capacitor employing such dielectric material and such electrode material is easily degraded in the sintering using the forming gas.
For example, in DRAM, after the formations of transistor, the capacitor, the wirings, the protection insulating film, etc., the sintering, i.e., heating the semiconductor substrate at the temperature of 400 to 450xc2x0 C. in the atmosphere of the forming gas is carried out to improve the characteristics of the transistor. Such forming gas is a mixture of hydrogen and nitrogen gases and contains the hydrogen gas at a capacity ratio of 3 to 5%. The sintering time is several tens minutes to several hours.
The sintering conducted under such conditions can improve the transistor characteristics, but causes such a problem that the dielectric material or the electrode material is degraded to thus increase the leakage current of the capacitor.
In Patent Application Publication (KOKAI) Hei 11-67905, for example, the sintering employing the forming gas is the process which is normally carried out in the semiconductor device regardless of the presence of the capacitor.
It is an object of the present invention to provide a manufacturing method of a semiconductor device including the sintering step which never degrades the characteristic of a capacitor.
According to the present invention, as is evident from the experiment, the sintering gas employed to improve the characteristic of the transistor formed on the semiconductor substrate is a mixture of nitrogen, hydrogen, and oxygen gases, the degradation of the capacitor formed on the semiconductor substrate seldom occurs.
It is preferable that the oxygen gas in the atmosphere in which the semiconductor substrate is placed at the time of sintering should be set to 0.01% to 5.0%. And, at the time of sintering, it is preferable that the heating temperature of the substrate is set to 300 to 600xc2x0 C.